"Quenching is the rapid cooling process from an elevated temperature. Compared to water and oil quench medium, high pressure and velocity gas is preferred to quench medium and high hardenability steel, with the potential to reduce distortion, stress and cracks. Currently, no standard test exists to characterize the gas quench steel hardenability and measure the performance of industrial gas quench furnaces. In this thesis, the fundamental difference between the liquid and gas quenching, heat transfer coefficient, was emphasized. It has been proven that gas quenching with constant HTC cannot generate the similar cooling curves compared to liquid quenching. Limitations on current gas quench steel hardenability tests were reviewed. Critical HTC, a concept like critical diameter, was successfully proved to describe the gas quench hardenability of steel. An attempt to use critical HTC test bar and measure the HTC distribution of gas quench furnace was made. Gas quenching, usually with slow cooling rate, may reduce hardness and Charpy impact toughness, compared to water and oil quenching. Lattice parameter and c/a ratio of as-quenched martensite in steel was measured using high resolution X-ray diffraction and Rietveld refinement. For AISI 4140, Charpy impact toughness decreases when the cooling rate decreases after quenching and tempering. Austenite percentage and carbon content in austenite is proposed as the dominated mechanism."

Electrical properties of thin film have been an issue of interest for a long time and there are many applications in contemporary industry. Interesting characteristics, such as a metal-insulator transition and superconductivity, were investigated and applied to manufacturing of various electrical devices. In this line of study, many experimental techniques have been introduced for precise measurement of the properties of thin film. Quench-condensation is one of the important techniques in the research of thin films. To facilitate this research, we built a quench-condensation apparatus which can be used for a variety of experiments. The apparatus was designed for the fabrication of ultra-thin film and the in-situ measurement at low temperature. The apparatus was shown to operate well for the fabrication of thin films while monitoring the growth in-situ. As a part of the preliminary research, we measured the electrical properties of aluminum thin films at liquid nitrogen temperature by using this apparatus. An investigation of the thickness dependent conduction properties was successively performed in-situ. Experimental data showed agreement with theory, in particular the electrical conduction model of Neugebaur and Webb.

Electrical properties of thin film have been an issue of interest for a long time and there are many applications in contemporary industry. Interesting characteristics, such as a metal-insulator transition and superconductivity, were investigated and applied to manufacturing of various electrical devices. In this line of study, many experimental techniques have been introduced for precise measurement of the properties of thin film. Quench-condensation is one of the important techniques in the research of thin films. To facilitate this research, we built a quench-condensation apparatus which can be used for a variety of experiments. The apparatus was designed for the fabrication of ultra-thin film and the in-situ measurement at low temperature. The apparatus was shown to operate well for the fabrication of thin films while monitoring the growth in-situ. As a part of the preliminary research, we measured the electrical properties of aluminum thin films at liquid nitrogen temperature by using this apparatus. An investigation of the thickness dependent conduction properties was successively performed in-situ. Experimental data showed agreement with theory, in particular the electrical conduction model of Neugebaur and Webb.

none

No description available.

No description available.

No description available.

Gas quench technology has been rapidly developed recently with the intent to replace water and oil quench for medium and high hardenability steel. One of the significant advantages is to reduce the distortion and stress, compared to water and oil quench. However, not like liquid quench, no gas quench steel hardenability test standard exists. The fundamental difference between liquid quench and gas quench is heat transfer coefficient. The workpiece with the same hardness after liquid and gas quench process may have different microstructure due to different cooling curves. The concept of equivalent gas quench heat transfer coefficient (HTC) is proposed to have the same cooling curve, microstructure and hardness when compared with liquid quench. Several influencing factors on steel hardenability have been discussed, such as austenizing temperature, heating rate, holding time, composition variation and grain size difference. The phase quantification by X-ray Diffraction and Rietveld Refinement method is developed to measure phase percentage for steel microstructure, including martensite, ferrite and carbides. The limitations and improvements of modified Jominy gas quench test are discussed. The fundamental limitation of Jominy gas quench test is that one gas quench condition cannot be used for both low hardenability steel and high hardenability steel at the same time. The same steel grade would have different hardenability curves under different gas quench conditions, which made it difficult to compare the hardenability among different steels. The critical HTC test based on Grossmann test is proposed to overcome the limitations. In the test, different gas quench HTC conditions are applied to the sample with the same geometry. After sectioning each bar at mid-length, the bar that has 50% martensite at its center is selected, and the applied gas quench HTC of this bar is designated as the critical HTC. This test has many advantages to take the place of modified Jominy gas quench test. Since one of the advantages of gas quench is greater process flexibility to vary cooling rates, gas marquenching technology is proposed to obtain martensite with less sever cooling rate and reduce the distortion and stress.

Techn. Hochsch., Diss., 2001--Aachen.

Le quench d'un système magnétique d'ITER est une transition irréversible d'un conducteur, de l'état supraconducteur à l'état normal résistif. Cette zone normale se propage le long du câble au cours du temps, en dissipant une grande quantité d'énergie. La détection se doit d'être suffisamment rapide afin de permettre une décharge de l'énergie magnétique et éviter un endommagement permanent du système. La détection primaire de quench d'ITER est basée sur la détection de la tension due au quench, qui est le moyen le plus rapide. L'environnement magnétique perturbé pendant le scenario plasma rend la détection de cette tension très difficile, à cause des hautes tensions inductives qu'il génère dans les bobinages. En conséquence, des compensations de tension sont nécessaires afin de discriminer la tension résistive due au quench.Une solution conceptuelle de la détection de quench basée sur la mesure des tensions est proposée pour les trois grands systèmes magnétiques d'ITER. Pour ceci, une méthodologie claire est développée, incluant le calcul classique selon le critère du point chaud, l'étude de la propagation de quench grâce au code commercial Gandalf, et l'estimation des perturbations inductives, grâce au développement du code TrapsAV. Des solutions adaptées sont proposée pour ces systèmes ainsi que les paramètres de cette détection, qui sont le seuil de détection (entre 0.1 V et 0.55 V) et le temps de discrimination (entre 1 s et 1.2 s). Les valeurs choisies, et en particulier le temps de discrimination, sont suffisamment élevées pour garantir la fiabilité du système, et pour éviter le déclenchement intempestif de décharges rapides non nécessaires. / The quench of one of the ITER magnet system is an irreversible transition from superconducting to normal resistive state, of a conductor. This normal zone propagates along the cable in conduit conductor dissipating a large power. The detection has to be fast enough to dump out the magnetic energy and avoid irreversible damage of the systems. The primary quench detection in ITER is based on voltage detection which is the most rapid detection. The very magnetically disturbed environment during the plasma scenario, makes the voltage detection particularly difficult, inducing large inductive components in the coils and voltage compensations have to be designed to discriminate the resistive voltage associated with the quench. A conceptual design of the quench detection based on voltage measurements is proposed for the three majors magnet systems of ITER. For this, a clear methodology was developed. It includes the classical hot spot criterion, the quench propagation study using the commercial code Gandalf and the careful estimation of the inductive disturbances by developing the TrapsAV code.Specific solutions have been proposed for the compensation in the three ITER magnet systems and for the quench detection parameters which are the voltage threshold (in the range of 0.1 V- 0.55 V) and the holding time (in the range of 1 -1.4 s). The selected values, in particular the holding time, are sufficiently high to ensure the reliability of the system and avoid fast safety discharges not induced by a quench which is a classical problem.